Lipophilicity

Lipophilicity (from Greek λίπος "fat" and φίλος "friendly"), refers to the ability of a chemical compound to dissolve in fats, oils, lipids, and non-polar solvents such as hexane or toluene. These non-polar solvents are themselves lipophilic (translated as "fat-loving" or "fat-liking")—the axiom that like dissolves like generally holds true. Thus lipophilic substances tend to dissolve in other lipophilic substances, while hydrophilic (water-loving) substances tend to dissolve in water and other hydrophilic substances.

Lipophilicity, hydrophobicity, and non-polarity can describe the same tendency towards participation in the London dispersion force as the terms are often used interchangeably. However, the terms "lipophilic" and "hydrophobic" are not synonymous, as can be seen with silicones and fluorocarbons, which are hydrophobic but not lipophilic.

Chemical bonding

Lipophilic substances interact within themselves and with other substances through the London dispersion force. They have little to no capacity to form hydrogen bonds. When a molecule of a lipophilic substance is enveloped by water, surrounding water molecules enter into an "ice-like" structure the greater part of its molecular surface, the thermodynamically unfavourable event that drives oily substances out of water. Being "driven out of water" is the quality of a substance referred to as hydrophob (water-avoiding or water-fearing). Thus lipophilic substances tend to be water-insoluble. They invariably have large o/w (octanol/water) partition coefficients.